Controlled-source electromagnetic (“CSEM”) surveying is a powerful tool for hydrocarbon exploration. To map resistivity anomalies that can be related to hydrocarbon fields, raw survey data (measurements of one or more components of the electric or magnetic fields) are processed, then interpreted. Interpreting CSEM data consists of developing a model of the earth's resistivity that is consistent with the measured CSEM data and with any other available geophysical or geological information. While they are not necessarily practiced in this order, interpretation typically includes the steps of:                Understanding which features of the data may properly be regarded as signal and which features as noise;        Understanding how the signal varies in space;        Understanding how the signal varies with frequency;        Understanding how the signal varies among the x, y, z components of the data, in both amplitude and phase;        Constructing approximate resistivity models of the earth in 1, 2 and 3 dimensions;        Constraining those models with additional information, such as well logs or seawater resistivity profiles; or structural information derived from seismic or gravimetric or magnetic data.        Forward-modeling synthetic electromagnetic field data based on those earth models and the source-receiver configurations in the measured data;        Comparing those actual and synthetic data to understand how the anomalies or misfits vary in space, among frequencies, or among data components;        Comparing synthetic data to synthetic data to understand how changes in the earth model impact synthesized data;        Modifying the earth model and re-synthesizing data;        Inverting the measured data; and,        Evaluating the resistivity models together with other geophysical measurements for evidence of hydrocarbon accumulations.        
Typically, CSEM data is collected by individual receivers (laid on the sea floor) that record the signal emitted by a transmitter towed a few meters above the sea floor (however, in some experiments, the transmitter can also be fixed). CSEM surveys can be large and complex. For example, a survey might involve 7 tow lines, 90 receivers, and 10 or more discrete frequencies. Each receiver may record up to 6 electric and magnetic field components. In addition, the CSEM data may have been processed in more than one way in order to improve some signals at the expense of others or to convey uncertainties present in the data. Furthermore, many synthetic data sets may be produced as part of the iteration cycle for reconciling the measured data with an earth resistivity model. Therefore, the CSEM interpreter faces the daunting bookkeeping challenge in ensuring that all of the measured data are explained in terms of a single resistivity model of the earth.
Some recent publications and patents address one or another part of these problems, or present final results with little discussion of the tools employed. Often, literature only presents final results. See, for instance U.S. Patent Publication 2005/0077902; and S. Ellingsrud et al., The Leading Edge 21, 972-982 (2002). There is a need for a tool that integrates the full process of interpreting the CSEM data.